Many cosmetic products are in the form of water-in-oil emulsions because they permit uniform application, and because they provide good coverage, as well as good skin feel, wear, and appearance. For example, many types of make-ups, such as, for example, foundation, mascara, eye-shadow, eye-liner, rouge, concealer, lipstick, lipcolor, and the like, often are in the form of water-in-oil emulsions. Generally, such products are used to apply color, mask imperfections, provide some visual effect, such as a glowing effect, and the like in order to enhance the beauty of the user. In addition, many types of pigmented sunscreens, or “particulate” sunscreens, are in the form of water-in-oil emulsions where the pigment is “invisible” and is included to protect the skin from potentially damaging sun rays, rather than to apply color to the skin to enhance beauty.
Despite the aesthetic and application attributes provided by such pigmented water-in-oil emulsion products, a significant problem with such products is that they tend to separate over time due to the presence of the pigment particulate, which is much heavier than the aqueous and oil phases. In this respect, although a typical water-in-oil emulsion that is absent pigment particulate generally will remain stable, the inclusion of the relatively heavy pigment particulate tends to destroy the emulsion because of the weight difference of the pigment as compared with the oil and aqueous phases. As a result, the aqueous phase, oil phase, and pigment particulate separate such that they no longer are uniformly distributed in the product's container. Generally, after packaging of the product, the water travels to the top of the container, creating a relatively clear surface layer, while the pigment travels to the bottom of the container. Although the user can attempt to compensate for the separation by shaking the container prior to application, it nevertheless is difficult for the user to achieve a uniform application, thereby diminishing the application and aesthetic qualities of the product.
Previous attempts to minimize separation in pigmented water-in-oil cosmetic products have not met with success. For example, one approach has been to include thickener, such as metal soaps and the like, to increase the viscosity of the product in an attempt to fix in place the water droplets and pigment in the continuous oil phase. However, the addition of such conventional thickeners to the water-in-oil emulsions only results in short-term benefits, and such products still tend to separate over time. In addition, separation in conventionally thickened formulations can be triggered in response to exposure to elevated temperatures, such as, for example, temperatures above about 40° C. Furthermore, enhancement of the thickness can diminish some of the product's aesthetic properties, such as its desired feel and its ability to be uniformly applied.
Another disadvantage with conventional water-in-oil emulsion cosmetic products relates to their manufacture. For example, such products typically require the use of pigment blends in order to produce a final color which may vary depending upon the desired tone of the user. However, conventional manufacturing techniques are inefficient because they do not permit the mixing of two or more water-in-oil emulsions of different colors because of the tendency of the emulsions to separate. In view of the size requirements of existing manufacturing equipment, conventional water-in-oil emulsion cosmetic products are prepared in one large batch with the pigments blended therein during processing. Thus, conventional manufacturing techniques for preparing pigmented water-in-oil emulsion products are ill-suited for making varying quantities of product, particularly lower quantities, because of the lack of versatility in manufacture caused by the difficulty in mixing more than one pigmented water-in-oil emulsion together.
Accordingly, it will be appreciated from the foregoing that there is a need in the art for a pigmented cosmetic composition comprising a water-in-oil emulsion that does not separate readily, particularly over time, while maintaining desired application, feel, coverage, wear, and appearance characteristics. There also is a need for a pigmented cosmetic composition that is able to remain stable even upon exposure to elevated temperatures. It will also be appreciated that there is a need for a method of preparing the cosmetic composition where two or more pigmented water-in-oil emulsions, for example, of differing colors, can be blended together to achieve a final product.